Fascioliasis is a neglected zoonotic human infection with global health importance, especially in the Peruvian highlands where the prevalence in children is among the highest in the world. Most infections by Fasciola are likely to be subclinical and can remain undiagnosed for many years. Case series of chronic fascioliasis have associated the infection with anemia and weight loss, which carry devastating consequences for children's cognitive development and productivity later in life. The epidemiology of these conditions associated with Fasciola is not well understood. Although, chronic inflammation has been postulated as the common underlying mechanism, the markers and clinical course of these complications have not been well described. We hypothesize that subclinical fascioliasis is the most common presentation in highly endemic areas and is responsible for complications rarely attributed to the parasite like anemia and malnutrition. We also hypothesize that chronic inflammation is responsible for these complications and that newly described markers will shed light into fascioliasis pathogenic mechanisms. To test these hypotheses we intend to perform a comprehensive evaluation of anemia and nutrition among children in the southern highlands of Peru. Through cross-sectional studies a large number of children will be screened for fascioliasis, anemia and malnutrition, and other intestinal helminths. A case-control study to define the mechanism of anemia will include iron studies and markers of inflammation (including a newly described marker called hepcidin that play a key role in anemia of chronic disease). Studies to evaluate the impact on nutrition and the mechanisms associated with weight lost will be performed (using Neuropeptide Y as a marker for negative shifts in energy balance). A one year cohort study to evaluate the severity of illnesses, response of anemia and malnutrition to treatment of fascioliasis and other helminths, and markers associated with fascioliasis will be performed. Our results will provide important epidemiologic and pathophysiologic information adding to the understanding of Fasciola associated anemia and malnutrition. The integration of this information with current disease interventions will lead to better planning and use of resources. But most importantly, will stress the need for early diagnosis and treatment of fascioliasis to avoid long term complications in children.